Capillary Condensation in Liquid-Crystal Colloids

We study capillary condensation between two spherical particles dispersed in the isotropic phase of a nematic liquid crystal. Within the Landau–de Gennes theory, we calculate interaction energies due to the formation of capillary bridges that reproduce experimental observations. Close to the critical point of the transition line separating the no-bridge from the bridge configuration, fluctuations in the particle cluster might be described by an effective two-state system. We show that the transition line vanishes for small particles and that the shape of the interaction potential depends on particle size.

Figure 1

Interaction energy in units of $\Delta f{a}^2{\xi }_r$ as a function of the reduced distance to contact $d/a$. The reduced particle radius is $a/{\xi }_r=35$ and temperature serves as parameter.

Figure 2

In a $\tau ,d$ diagram for a reduced particle radius $a/{\xi }_r=35$, the first-order transition line between the no-bridge and the bridge configuration ends in a critical point. The insets depict the capillary bridges at different locations on and beyond the transition line.

Figure 3

In a $\tau ,a$ diagram, the line of critical points separates regions where the transition between the no-bridge and the bridge transition is either discontinuous or smooth. The inset shows interaction profiles for different particle radii at $\tau =1$. The solid line is a fit to a Morse potential.